Foods that are high in insoluble fiber, lactose, and sugars may trigger symptoms of ulcerative colitis. Working with a healthcare professional may help you identify which foods to avoid.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease (IBD) that can affect your colon and rectum.

Your diet and gut bacteria may play a role in the onset of UC symptoms.

Keep reading to discover foods that commonly trigger symptoms of UC.

Whole grain products are typically high in fiber, which may be hard to digest if you have UC.

A low fiber diet is recommended during a flare-up because it may help reduce the frequency and volume of bowel movements.

Whole grain flour is high in fiber because it hasn’t had the germ or bran removed. Other whole grain starches still have the fibrous endosperm, germ, and bran that may irritate UC and trigger a flare-up.

Below are whole grain foods that you may want to avoid during a flare-up:

Whole grain flourOther whole grain starches
• breads
• cereals
• pastas
• noodles
• brown rice
• quinoa
• buckwheat
• oats
• wild rice
• plain barley
• millet
• wheat berries
• bulgur wheat
• spelt

Better options during flare-ups include foods made from refined grains or enriched white flour, such as white bread, pasta, and rice. Flour is “enriched” when nutrients lost during the germ and bran removal process are replaced.

You should avoid foods high in fiber only during flare-ups. A diet that’s high in fiber, lean protein, and vegetables could actually help prevent symptom flare-ups and maintain remission.

Whole nuts may trigger symptoms of UC. This may be due to their high sulfur content, which could make them hard to digest.

It’s best not to consume the following nuts:

  • hazelnuts
  • pecans
  • cashews
  • almonds
  • macadamia nuts
  • peanuts
  • pistachios

Although it’s best to avoid most nuts during flare-ups, eating walnuts during remission periods may be beneficial.

The authors of a 2023 review suggest that walnuts may have anti-inflammatory and antimicrobial properties and could help prevent UC and prevent damage to the mucous membrane in your stomach.

Seeds contain insoluble fiber, which doesn’t dissolve in water. This may increase the time it takes for food to move through your digestive system, as well as the frequency, volume, and severity of your bowel movements.

Seeds to avoid include:

  • sesame seeds
  • flaxseed
  • millet
  • pine nuts
  • sunflower seeds
  • pumpkin seeds
  • wild rice

Legumes, including beans, lentils, and peas, are high in fiber and protein. However, they’re notorious for causing bloating and gas due to their indigestible sugars.

It’s best to avoid the following if you’re experiencing a flare-up:

  • all beans, including chickpeas
  • adzuki beans
  • soy nuts, including soybeans and edamame

Many fruits and vegetables contain large amounts of fiber, which can cause symptom flare-ups.

It’s best to avoid fruits and vegetables that:

  • are raw or dried
  • have a peel or skin
  • are cruciferous, such as broccoli and cauliflower
  • have seeds that can’t be removed, such as berries

You can still consume fruits and vegetables. However, the following preparations may be best:

  • Skinned and peeled: Peels and skins may be hard to digest due to their insoluble fiber. Be sure to peel and skin fruits and vegetables before eating them.
  • Cooked: Raw vegetables and some raw fruits can be hard to digest. After skinning or peeling, cook the foods until very soft. Applesauce is a great way to eat apples, and soups are an easier way to digest vegetables.
  • Canned: Canned fruits and vegetables may be easier to digest than fresh, uncooked vegetables. But make sure they’re packed in water or in their own juice to avoid excess sugar, and discard any skin.

It’s important to keep vegetables and fruits in your diet because they provide many important nutrients.

Lactose is a sugar found in many dairy products, such as milk, cheese, and yogurt.

A 2020 study found that people with UC were 2.7 times more likely to develop lactose intolerance than those who didn’t have UC.

Symptoms of lactose intolerance may be similar to those of UC, such as diarrhea, bloating, and abdominal pain.

If you suspect that dairy may be triggering your symptoms, you can try removing all types of dairy from your diet for 4 weeks.

A healthcare professional may also suggest you follow an elimination diet. This can help you identify and remove foods that trigger or worsen your symptoms.

Sugary products such as candies, juices, and baked goods can all contribute to UC flares, according to the Crohn’s and Colitis Foundation (CCF). A high sugar diet can also make you more susceptible to UC flares when you’re in periods of remission.

You may be tempted to eat sugar-free foods. However, these often contain sugar alcohols such as mannitol and sorbitol, which your body cannot digest.

Foods containing nonabsorbable sugars include:

  • sugar-free gum
  • sugar-free drinks
  • fruits such as peaches, pears, and plums

Eating a low fat diet may help reduce your symptoms if you have UC or reduce your risk of developing UC if you don’t have it.

Limiting the following high fat foods can help you manage UC in remission and reduce the severity of flares:

  • butter
  • coconut oil and other oils
  • margarine
  • cream
  • fried foods

The authors of a 2017 review found that soft drinks increased the risk of developing UC. These types of drinks include soda and other carbonated beverages that contain a lot of sugar and artificial sweeteners.

The authors also found that alcohol and coffee didn’t affect UC and that drinking tea may actually help decrease symptoms.

The CCF recommends avoiding alcohol because it may trigger UC symptoms.

Similarly, the authors of a 2021 review suggest that drinking alcohol may increase intestinal inflammation, worsen UC symptoms, and increase the risk of UC relapse. Alcohol may also interact negatively with medications used for treatment.

However, more research is needed on the relationship between alcohol and UC.

The authors of the 2017 review mentioned above found no association between alcohol and UC.

According to the CCF, spicy foods can worsen UC flares. However, research in this area is limited.

A 2019 review suggests that capsaicin — the active component in chiles that makes them spicy — may actually reduce intestinal inflammation and IBD symptoms.

Gluten is a protein in wheat, rye, and barley. It’s found in common foods such as bread and pasta and is often added to prepared foods such as condiments, sauces, and soups.

Gluten intolerance is becoming more common in people with digestive symptoms.

However, a 2022 study found that gluten didn’t worsen symptoms in people with UC or increase the risk of developing UC in people who didn’t have it.

Consult a healthcare professional if you suspect that gluten may be a symptom trigger for you. You can try an elimination diet for 4 weeks or try eating gluten-free foods.

Eating doesn’t have to be boring when you’re living with UC.

You can include the following foods in your diet:

  • low fiber fruits
  • refined white carbohydrates
  • lean proteins
  • well-cooked, skinless vegetables
  • skinless, seedless fruits

To increase your chances of remission, gradually reintroduce high fiber foods. Fiber protects the health of your colon tissue and your gut bacteria.

Speak with a healthcare professional if you have an allergy or a food intolerance. They’ll be able to help you develop a nutrition plan that’s right for you.

What foods can trigger ulcerative colitis?

Foods that may trigger symptoms of UC include:

  • whole grain products
  • nuts
  • legumes
  • high fat foods
  • spicy foods
  • carbonated drinks
  • alcohol
  • lactose
  • uncooked or cruciferous vegetables
  • fruits and vegetables with a peel

Living with UC can make eating and drinking a challenge because certain foods may trigger flare-ups.

Avoiding common trigger foods or trying an elimination diet can help you manage your symptoms.

A health professional such as a registered dietitian can help you develop a diet that works best for you, since not everyone with UC will do well on the same diet.